Process for preparing a free-flowing, modified polypropylene powder

ABSTRACT

A process for preparing a free-flowing powder is disclosed, which powder is useful in primer compositions. The process comprises the steps of (a) dissolving a polar group-containing modified propylene polymer (MPP) at an elevated temperature in a solvent for the MPP, (b) cooling the solution to precipitate particles of the MPP, (c) collecting the precipitated particles by simultaneously centrifuging and spraying the particles with a liquid capable of removing the solvent from the particles and which is also a solvent for a film forming resin, such as an epoxy, which is present in the primer composition, (d) continuing step (c) until substantially all of the solvent for the MPP has been removed from the particles, and (e) collecting the resulting powder, which has an average particle size of less than about 5 microns.

This application is a divisional of copending application Ser. No.07/053,439 filed May 22, 1987, which in turn is a continuation ofapplication Ser. No. 06/894,081 filed Aug. 6, 1986, which in turn is acontinuation of Ser. No. 06/681,153 filed Dec. 13, 1984, all nowabandoned.

This application is also a substitute for application Ser. No.07/221,695 filed July 20, 1988, now abandoned.

BACKGROUND OF THE INVENTION

This invention relates to primer compositions which are homogeneous,fluid, uncured suspensions of discrete particles of a modified propylenepolymer in a film forming resin and methods for making and using theseprimers.

Primer compositions are frequently used to bond a polypropylene layer toa variety of substrates, including various metals. These primers oftencontain particles of a modified propylene polymer in an organic liquid,such as kerosene or Isopar, and sometimes also include a film formingresin such as an epoxy resin. However, these primer compositions sufferfrom several drawbacks. For instance, those which do not contain thefilm forming resin may not form a uniform coating on the surface to bebonded, resulting in poor bonding. On the other hand, when the filmforming resin is employed, it is often incompatible with the organicsolvent which contains the modified propylene polymer making itdifficult, if not impossible, to blend enough of the modified propylenepolymer particles into the film forming resin to make a useful primercomposition.

It has now been unexpectedly found that a primer composition consistingessentially of a homogeneous, fluid, uncured suspension of discreteparticles of a polar group-containing modified propylene polymer in afilm forming resin material, the particles having an average particlesize of less than 5 microns, and the primer composition beingsubstantially free of solvent for the polar group-containing modifiedpropylene polymer eliminates the drawbacks encountered with currentlyused primers and provides superior bonding properties.

SUMMARY OF THE INVENTION

In accordance with the present invention there is provided a primercomposition consisting essentially of a homogeneous, fluid, uncuredsuspension of discrete particles of a polar group-containing modifiedpropylene polymer in a film forming resin material, the particles havingan average particle size of less than 5 microns, and the primercomposition being substantially free of solvent for the polargroup-containing modified propylene polymer.

There is also provided in accordance with this invention an apparentlydry powder comprising about 25% to about 45% of discrete, free flowing,non-agglomerating particles of a polar group-containing modifiedpropylene polymer and about 55% to about 75% of a solvent for a filmforming resin material, all percentages being by weight based on thetotal weight of the powder.

There is further provided in accordance with this invention a processfor preparing an apparently dry powder comprising about 25% to about 45%of particles of a polar group-containing modified propylene polymer andabout 55% to about 75% of a solvent for a film forming resin material,wherein all percentages are by weight based on the total weight of thepowder, said process comprising dissolving a polar group-containingmodified propylene polymer at an elevated temperature in a solvent forthe polar group-containing modified propylene polymer, cooling thesolution to precipitate particles of the polar group-containing modifiedpropylene polymer, collecting the precipitated particles bysimultaneously centrifuging and spraying the particles with a liquidwhich is capable of removing the solvent from the particles and which isalso a solvent for a film forming resin material, continuing saidcentrifuging and spraying until substantially all of the solvent for thepolar group-containing modified propylene polymer has been removed fromthe particles, and collecting the resulting powder.

The present invention further provides a process for laminating apolypropylene layer to a substrate, said process comprising applying tothe substrate a primer layer consisting essentially of a homogeneous,fluid, uncured suspension of discrete particles of a polargroup-containing modified propylene polymer in a film forming resinmaterial, the particles having an average particle size of less than 5microns, and the primer being substantially free of solvent for thepolar group-containing modified propylene polymer, curing the primerlayer, contacting the thus-primed substrate with the polypropylenelayer, and bonding the thus-formed laminate by applying heat, pressureor both to the laminate until bonding occurs. The present invention alsoprovides laminates produced by this process.

This invention further provides a process for bonding two articlescomprising:

a. Applying to the surface of each article a layer of a primercomposition consisting essentially of a homogeneous, fluid, uncuredsuspension of discrete particles of a polar group-containing modifiedpropylene polymer in a film forming resin material, the particles havingan average particle size of less than 5 microns and being present in anamount of at least about 3% by weight based on the nonvolatile contentof the primer composition, said primer composition being substantiallyfree of solvent for the polar group-containing modified propylenepolymer;

b. curing the thus-formed primer layers; and

c. bonding articles by contacting the two cured primer layers andapplying heat, pressure or both until bonding occurs. The presentinvention also provides bonded articles produced by this process.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In accordance with one aspect of this invention, there is provided aprimer composition consisting essentially of a homogeneous, fluid,uncured suspension of discrete particles of a polar group-containingmodified propylene polymer in a film forming resin material, theparticles having an average particle size of less than 5 microns and theprimer composition being substantially free of solvent for the polargroup-containing modified propylene polymer.

Polar group-containing modified propylene polymers suitable for use inthe present invention are polymers obtained by introducing a polar groupinto a propylene polymer by some suitable means. The "polar groups"which are incorporated in the modified propylene polymer include, forexample, atoms or atomic grouping which have good affinity for an epoxyresin or other film forming resin material. The preferred polar group ismaleic anhydride.

The amount of the polar groups in the modified propylene polymer must besufficient to provide adhesion between the polar group-containingmodified propylene polymer and the film forming resin material in theprimer composition when the primer composition is cured. There is nocritical upper limit to the amount of polar groups on the propylenepolymer although if this amount becomes too high the mechanicalproperties of the modified propylene polymer will degrade to the pointwhere the polymer no longer behaves like a propylene polymer. Anespecially suitable polar group useful in the practice of this inventionis a maleic anhydride group.

The preferred polar group-containing modified propylene polymers, i.e.maleic anhydride modified propylene polymers, are commerciallyavailable, for example, from Hercules Inc under the trademarkHercoprime.

The polar group-containing modified propylene polymers are employed inthe primer compositions of this invention in the form of discrete,essentially spherical particles having an average particle size of lessthan 5 microns. In another aspect of this invention, there is provided aparticularly preferred method of preparing these particles. Inaccordance with that aspect of this invention, the polargroup-containing modified propylene polymer is dissolved at an elevatedtemperature in a normally liquid organic material which is a solvent forthe modified propylene polymer. The term "solvent" as used in thiscontext refers to normally liquid organic materials which are capable ofdissolving the modified propylene polymer. Generally, such dissolutioncan be accomplished only at elevated temperatures. However, the term"solvent" as used herein refers to these liquid organic materials bothwhen they are employed under circumstances which cause dissolution ofthe polymer, e.g., elevated temperature, or under circumstances which donot cause the polymer to dissolve, e.g., room temperature. Examples ofsolvents for the polar group-containing modified propylene polymerinclude, but are not limited to, paraffin hydrocarbons, aromatichydrocarbons and halogenated hydrocarbons. Preferred solvents includen-decane, hexadecane, chlorobenzene, cyclohexane, xylene (mixed),n-heptane, Isopar H and Isopar M (mixtures of isoparaffinichydrocarbons), and Solvesso 150 (a mixture of aromatic hydrocarbons).Normally, the modified propylene polymer will be dissolved in thesolvent at the temperature which is just high enough to cause themodified propylene polymer to dissolve. This temperature can varydepending upon the particular solvent employed, about 120° C. being therequisite temperature for the preferred solvent, Isopar M. As notedbelow, excessive heating of the solvent during dissolution can result inundesirable particle sizes for the recrystallized modified propylenepolymer.

The modified propylene polymer is dissolved in the hot solvent to aconcentration of about 1% to about 15%, preferably about 5% to about10%. Concentrations higher than about 15% will not produce particleswithin the desired particle size range. After the modified propylenepolymer is completely dissolved, the resulting solution is cooledquiescently to room temperature which causes the modified propylenepolymer to recrystallize in the form of particles.

It is important to note at this point that the size of the particlesresulting from the above procedure is dependent upon a number offactors, principally the temperature of the solvent and theconcentration of the modified propylene polymer in the solvent Forexample, the small particle sizes (5 microns and smaller) of thisinvention are achieved by heating the solvent only as much as is neededto dissolve the modified propylene polymer. Heating the solvent tohigher temperatures tends to cause fewer, larger particles to form. Byway of example, if Isopar M is the solvent, heating the solvent to about120° C. will produce particles in the desired range whereas temperaturesin excess of about 137° C. produce particles which are too large.

Another factor which controls particle size is the concentration of themodified propylene polymer in the hot solution. To some degree, theeffects of concentration on particle size are independent of thetemperature of the solvent. For instance, in the example cited above, ifthe Isopar M is at the preferred temperature of 120° C., but theconcentration is above about 15%, the "particles" which form, uponcooling are so close together (i.e., so many particles are contained ina relatively small volume of solvent) that the particles willagglomerate and "clump" into a semi-solid material rather than remainingas discrete particles. At lower concentrations, however, the smallparticles which form upon cooling are dispersed sufficiently in arelatively large volume of solvent so agglomeration is kept to aminimum.

The recrystallized particles obtained from the above-described methodare then collected and subjected to shear (to separate weaklyagglomerated particles) to form a dispersion of the particles in the nowcool solvent. This dispersion must be filtered to remove the solvent andcollect the particles in the form of an apparently dry, free-flowingpowder.

Considerable difficulty was encountered in attempts to remove to lowlevels the solvent from the particles. Standard filtration techniquesproved ineffective for removing the solvent to the low levels requiredby this invention. Even centrifuging did not sufficiently separate thesolvent from the particles. Finally it was discovered that if theparticles were centrifuged in a drum and simultaneously sprayed with aliquid capable of removing the solvent from the particles, and thisprocedure continued or repeated until the desired amount of solvent isseparated from the particles, a powder was produced which wassubstantially free of solvent for the modified propylene polymer. Asused herein the term "substantially free of solvent for said polargroup-containing modified propylene polymer" means that the compositioncontains less than about 3% to about 5% solvent for the modifiedpropylene polymer based on the weight of the modified propylene polymer.The liquid capable of removing the solvent from the particles may alsobe added to the solvent/particle dispersion after recrystallization ofthe particles, but prior to centrifuging the dispersion. This allows thesolvent to be removed from the particles at a much faster rate, perhapstwo to three times faster than without such liquid being present.

By preparing the modified propylene polymer according to theabove-described process an apparently dry, free flowing powder can beproduced which is substantially free of solvent for the modifiedpropylene polymer. However, it was quite unexpectedly found that theresulting powder, though dry in appearance, actually contains asubstantial amount of the liquid used to remove or displace the solventfor the modified propylene polymer. By way of illustration, a typicalproduct which contained about 15% by weight of modified propylenepolymer and 85% by weight solvent for the polymer prior to centrifugingand spraying yielded a final powdery product which was about 40% byweight modified propylene polymer, only about 3% by weight solvent ofthe resin, and a quite unexpected 57% by weight of the liquid used toremove the polymer solvent.

While the powder by the above process could be dried to remove theliquid used to remove the polymer solvent, it can be particularlyadvantageous to allow this liquid to remain part of the powder system.For example, if it is intended that the powder produced by the aboveprocess is to be dispersed in a film forming resin material, then theliquid used to remove the polymer solvent can be selected so that itwill not only remove the polymer solvent, but will also be a solvent forthe film forming resin material. The presence of this liquid in thepowder system greatly enhances the ability of the powder to disperse inthe film forming resin material when compared to modified propylenepolymer powders which do not contain such a liquid. Also, the presenceof the liquid in the powder reduces dusting which would otherwise be apotential safety hazard.

Examples of liquids which may be used to remove the polymer solventinclude, but are not limited to, methyl ethyl ketone (MEK),cyclohexanone and the like.

As noted above, the powder produced by the process of this invention issubstantially free of solvent for the modified propylene polymer. Thisresults in several advantages over modified propylene polymer powders orparticles which are dispersed in solvent for the polymer or whichcontain substantial amounts of such solvent, i.e., more than about 5%.The presence of substantial amounts of such solvents can lead to severalproblems, such as incompatibility with the film forming resin materialor other components employed in a primer composition containing thepowder. Also, if a large amount of the solvent for the modifiedpropylene polymer is present in the primer when it is cured at elevatedtemperature, air pollution problems can result from the release of thesolvent. These problems are avoided or overcome by the powders producedby the process of this invention because they are substantially free ofsuch solvents. This advantage is particularly pronounced where it isdesirable to introduce large amounts of modified propylene polymerparticles into a film forming resin material. Heretofore, it wasnecessary to introduce large quantities of polymer solvent into the filmforming resin material along with the particles. However, large amountsof polymer solvent are often incompatible with the film forming resinmaterial which can cause phase separation of the materials.

The lack of polymer solvent in the powders of this invention also leadsto several economic advantages over those systems which require largeamounts of the solvent to be present. For instance, the process by whichthe powders of this invention are made permits the solvent to berecycled rather than merely lost by evaporation upon curing. Also,shipping and handling costs are substantially reduced because largequantities of solvent need not be handled and shipped along with thepowder.

In another aspect, this invention provides primer compositionsconsisting essentially of a homogeneuos, fluid, uncured suspension ofdiscrete particles of a polar group-containing modified propylenepolymer in a film forming resin material, the particles having anaverage particle size of less than 5 microns, and the primer compositionbeing substantially free of solvent for the polar group-containingmodified propylene polymer.

The particles of polar group-containing modified propylene polymeruseful in the primer composition of this invention are prepared from thepreviously described modified propylene polymer by the processpreviously described, and have an average particle size of less than 5microns. It has quite unexpectedly been found that, for a fixed amountof modified propylene polymer in primer compositions, smaller particlesize of the modified propylene polymer results in dramatically increasedbond strength when the primer composition is used to bond apolypropylene layer to a substrate. It has also been observed thatlarger particles (i.e. larger than about 5 microns) may not provide auniform layer when the primer is applied to the surfaces to be bondedand subsequently cured, with a consequent decrease in bondingperformance.

It has now been discovered that small particle sizes, i.e., less thanabout 5 microns, provide primer compositions which form a uniform layeron the surface to be bonded and enhance bond strength. As noted above,these small particle sizes provide primer compositions which, at a fixedamount of modified propylene polymer, have better bonding strength thanprimers containing larger particles. Another benefit of the smallerparticle sizes is that bond strengths equivalent to those achieved withlarger particles can be attained with a lower amount of the smallparticle size modified propylene polymer.

The film forming resin materials useful in the primer compositions ofthis invention are thermosetting resins, preferably epoxy resins. Theepoxy resins useful in this invention are polymeric reaction products ofpolyfunctional halohydrins with polyhydric alcohols, e.g. polyhydricphenols. A typical epoxy resin useful in the primer compositions of thisinvention has the structural formula: ##STR1## wherein n represents thenumber of molecules condensed. Typical polyfunctional halohydrins areepichlorohydrin, glycerol dichlorohydrin, and the like. Typicalpolyhydric phenols are resorcinol and a 2,2-bis(4-hydroxyphenyl)alkane,the latter resulting from the condensation of phenols with aldehydes andketones, including formaldehyde, acetaldehyde, propionaldehyde, acetone,methyl ethyl ketone and the like, which result in such compounds as2,2-bis(4-hydroxyphenyl) propane and like compounds.

The epoxy resins useful in this invention generally require a curingagent which causes crosslinking of the resin upon curing. A wide varietyof these curing agents are known in the epoxy resin art, generallyfalling within the categories of polyfunctional primary and secondaryamines, dibasic acids or acid anhydrides, carboxylic acid amides,methyolated melamines, blocked isocyanates, dicyandiamide and itsderivatives, carboxylic acid dihydrazides, imidazoline, imidazole, andsalts of imidazoline or imidazole. Examples of these curing agentsinclude, but are not limited to diethylene triamine, diethylaminopropylamine, adipic acid, sebacic acid, phthalic acid, trimellitic acid,maleic anhydride, phthalic anhydride, trimellitic anhydride, itaconicanhydride, tetrahydrophthalic anhydride, pyromellitic anhydride, theaddition product of dimeric acid with triethylenetetramine, methyletherified hexamethylolmelamine, epsilon-caprolactam-blocked isophoronediisocyanate, cresol-blocked tolylene diisocyanate-trimethylolpropaneadduct, 2,6-xylenyl biguanide and adipic acid dihydrazide.

The amount of curing agent required can vary widely depending upon theparticular epoxy resin and curing agent employed. This amount will,however, depend upon two factors. The first is the degree of curedesired; the second is the desired cure rate.

It is believed that, when the primer compositions of this invention arecoated onto a substrate, the modified propylene polymer particlesmigrate to the surface of the film forming resin where, upon heating,they melt and form a continuous, uniform layer of modified propylenepolymer. It is, therefore, essential that the film forming resin notcure before the particles can reach the surface of the resin layer, forto do so would trap the particles in the cured resin and prevent theircontact with any material subsequently applied to the coated substrate.Thus, the curing agent and the amount employed must be chosen so thatthe cure rate is slow enough to permit substantially all of the modifiedpropylene particles to reach the coating layer surface prior to curingof the film forming resin. In this regard, the so-called "latent" curingagents are particularly advantageous since they prevent premature curingof the resin.

The modified propylene polymer particles may be added to the filmforming resin material by simply stirring the particles into the filmforming resin material using, for example, conventional paint mixingequipment.

Generally, the modified propylene polymer particles are employed in theprimer compositions of this invention in an amount which will produce auniform, continuous layer of modified propylene polymer at the surfaceof the cured primer layer. While this minimum amount varies withparticle size, it will generally be in the range of at least about 3% byweight based on the nonvolatile content of the primer. Amounts greaterthan 30% provide several advantages, such as the ability to bond twometal surfaces without the use of an intermediate polypropylene layer.One unexpected advantage provided by this invention is that the modifiedpropylene polymer powders of the invention are so readily dispersed inthe film forming resin material that very high concentrations of thepowder in the film forming resin material can be achieved. Thus, primercompositions containing as much as 50% or more modified propylenepolymer powder can be easily made. These large concentrations ofmodified propylene polymer are particularly desirable when the primercomposition is employed to bond two substrates without the use of anintermediate polypropylene layer or when the primer composition is usedsimply to provide a chemically resistant coating of modified propylenepolymer on the surface of a substrate.

There is no critical upper limit for the amount of modified propylenepolymer in the primer compositions of this invention, the maximum amountbeing determined only by that amount of modified propylene polymer whichwill disperse in the film forming resin and still produce a primer whichcan be coated onto and bond to a substrate.

The primer compositions are used in accordance with this invention bycoating them on a substrate, heating the primer coating at an elevatedtemperature until the modified propylene polymer particles melt and forma uniform, continuous layer on the surface of the primer, and thencuring the film forming resin material. (This entire procedure isreferred to herein simply as "curing" the primer composition). Thetemperature to which the primer is heated may vary somewhat, but must beat least high enough to cause the modified propylene polymer particlesto melt. Generally, this temperature will be about 380°-400° C.

The primer compositions of the present invention are primarily usefulfor bonding a polypropylene surface to a substrate. The substrate may beany material to which the film forming resin will bond and which willwithstand the temperature required to cure the primer. Useful substratematerials include, but are not limited to wood, glass, metals and manyplastics.

The laminates of the present invention are made by applying a layer ofthe primer composition of this invention to the surface of a substratelayer, curing the primer composition and contacting the thus-primedsubstrate layer with the layer to which it is to be bonded(polypropylene or another primed surface) and bonding the two layers byapplying heat and pressure to the thus-formed laminate until bondingoccurs.

Particularly useful laminates can be made in accordance with thisinvention by bonding two layers of substrate together by means of anintermediate layer of polypropylene. Such a "sandwich" is made bycoating one surface of each substrate layer with a layer of the primercomposition of this invention, curing each primer layer, placing thepolypropylene layer between the primed substrate layers (with the curedprimer layer on each substrate facing the polypropylene layer) andbonding the primed substrates to the polypropylene layer.

An alternative to the substrate-polypropylene-substrate "sandwich" isprovided by simply coating one surface of each substrate layer with alayer of the primer composition of this invention, curing the primer(which forms a surface layer of modified propylene polymer on eachsubstrate) and bonding the two substrate layers (with the primedsurfaces facing each other) directly to one another. While thisalternative does not produce bond strengths as high as when anintermediate layer of polypropylene is used, it does provide sufficientbond strength for some applications, e.g. bonding packaging films ormaking a peelable bond, and does eliminate the need for the intermediatepolypropylene layer.

EXAMPLE 1

A maleic anhydride-modified polypropylene powder (Hercoprime A sold byHercules, Inc.) is added to Isopar M (an isoparaffinic solvent) which isthen heated to about 135°-142° C. The resulting mixture is maintained atthis temperature until all of the maleic anhydride-modifiedpolypropylene dissolves. The resulting solution is then poured onto amoving, chilled stainless steel belt and left on the belt until it coolsto about 49°-70° C. During this time the maleic anhydride-modifiedpolypropylene recrystallizes in the Isopar M. The resulting product isscraped off the belt in the form of weakly agglomerated particles ofmaleic anhydride-modified polypropylene dispersed in the Isopar M. Thisproduct is then subjected to shear and fluidization and homogenized(Gaulin homogenizer, 3000-4000 p.s.i.) to break apart the agglomeratedparticles. The solids content of the resulting product is then adjustedto a desired level and the product is homogenized again, resulting in aproduct which has essentially discrete particles of the modifiedpolypropylene (average particle size less than 5 microns) dispersed inIsopar M which has a viscosity (Brookfield) of about 100-300 centipoiseand is about 15% solids.

One drum of the above product is placed into a holding tank and agitatedto prevent settling of the particles. About one half of this product isthen centrifuged in a Tolhurst centrifuge (36 inch diameter drum) whichis lined with a heavy, tightly woven filter bag. After about 40 minutesof centrifuging the filter cake is white and the filtrate is coming outof the machine at a rate of about 156 grams/minute. After about 50minutes of centrifuging about 75.5 pounds of Isopar M has beencollected. The filter cake is then sprayed with about 17 pounds ofmethyl ethyl ketone (MEK) and centrifuged until the rate of filtrateremoval slows to a trickle. The filter cake is then sprayed again withMEK (about 16 pounds) and spun until the rate of filtrate removal slowsto a trickle. The resulting filter cake is about 60 mm thick with a dryband of about 45 mm on the inside of the cake and a darker, moist bandof about 15 mm on the outer portion of the filter cake.

EXAMPLE 2

The remainder of the drum of Isopar M/modified polypropylene productused in Example 1 is centrifuged by first adding 100 pounds of MEK tothis product and mixing until uniform. The resulting mixture is thenplaced in the centrifuge and spun at about 700 rpms. The resultingfilter cake is sprayed twice with MEK in the same manner as the firstrun. Upon completion of the centrifuging the filter cake is examined andfound to have a dark outer band of material about 1 cm thick with theremainder of the material being dry and snow white. The dry portion ofthe filter cake is tested for solid content and found to contain about41.5% solids and, though apparently dry, about 58.5% solvent. GCanalysis indicates that the "dry" filter cake is about 53.1% MEK, about4.7% Isopar M and about 42.2% modified polypropylene.

EXAMPLE 3

A primer composition is prepared from the "dry", snow white product ofExample 2 which is 53.1% MEK, 4.7% Isopar M and 42.2% modifiedpolypropylene. The primer composition contains:

22.5 grams snow white filter cake

84.0 grams of a solution of aminoplast cured bisphenol A epoxy resin(R-287 epoxy resin sold by Inmont Corp.)

36.7 grams MEK

The resulting primer composition contains 33% solids.

The primer composition is applied to two clean 1 inch wide aluminum (25mil) strips and baked in an oven at about 400° F. for about 2 minutes tocure the primer. A laminate is then formed by applying one aluminumstrip to each side of a 50 mil thick strip of EPDM-modifiedpolypropylene with the primed surface of the aluminum facing thepolypropylene "core". The resulting laminate is then pressed together atabout 390° F. at a pressure of about 5-10 p.s.i for about 1 minute. Thepeel strength of the resulting bonded laminate is very high with failureoccurring about 10 mils into the 50 mil polypropylene core. Peelstrength values range between about 105-123 lbs/lineal inch. Failure is100% cohesive.

EXAMPLE 4

A primer composition is prepared by placing the following ingredients ina suitable container:

1162.8 gms of a solution (43% solids) of aminoplast cured bisphenol Aepoxy resin (R-287 epoxy resin sold by Inmont Corp.)

1184.8 gms modified polypropylene filtercake prepared as in Example 2(42.2% solids)

682.4 gms MEK

An additional 90 gms MEK is added to the container and the resultingmixture is sheared until homogeneous. The mixture is then passed oncethrough a Gaulin homogenizer.

The resulting primer composition is applied with a No. 13 wire wound rodto one surface of each of two pieces of clean 4 mil aluminum foil. Bothpieces of coated foil are then baked at about 405° F. for about 2minutes. One piece of foil is then placed on top of the other with thecoated surfaces facing each other and the two foil pieces are bonded bypressing together at a pressure of about 40 psi and a temperature ofabout 425° F. for about 2.5 seconds. The resulting laminate has a peelstrength or about 2800-3000 gm/inch.

The primer composition is also applied to 13 mil aluminum foil with aNo. 21 wire wound rod. The thus-coated foil is then baked for about 2minutes at about 405° F. Strips one inch wide and three inches long arecut from the foil and heat sealed (primed surfaces facing each other) atabout 420° F., 40 psi for about 2.5 seconds. The resulting laminates aretested in an Instron Model 1123 at one inch/minute jaw separation and 20pound full scale load. The results are as follows:

    ______________________________________                                        Overlap Width of Bonded Area                                                                       Peel Strength                                            ______________________________________                                        13/16 inch           13.5 lbs/in.                                             14/16 inch           15.3 lbs/in.                                             ______________________________________                                    

I claim:
 1. A process for preparing a free-flowing powder comprisingabout 25% to about 45% of particles of a polar group-containing modifiedpropylene polymer and about 55% to about 75% of a solvent for a filmforming resin material, wherein all percentages are by weight based onthe total weight of the powder, said process comprising:a. dissolving apolar group-containing modified propylene polymer at an elevatedtemperature in a solvent for the polar group-modified propylene polymer,b. cooling the solution to precipitate particles of the polargroup-containing modified propylene polymer, c. collecting theprecipitated particles by simultaneously centrifuging and spraying theparticles with a liquid which is capable of removing the solvent fromthe particles and which is also a solvent for a film forming resinmaterial, d. continuing said centrifuging and spraying untilsubstantially all of the solvent for the polar group-containing modifiedpropylene polymer has been removed from the particles, and e. collectingthe resulting powder.
 2. A process according to claim 1 wherein thepolar group-containing modified propylene polymer is maleic anhydridemodified polypropylene.
 3. A process according to claim 1 wherein thesolvent for the polar group-containing modified propylene polymer is amixture of isoparaffinic hydrocarbons.
 4. A process according to claim 1wherein the liquid which is capable of removing the solvent from theparticles is methyl ethyl ketone.
 5. A process according to claim 1wherein the powder produced and collected in step (e.) has an averageparticle size of less than about 5 microns.
 6. A process for preparing afree-flowing powder comprising about 25% to about 45% of particles of apolar group-containing modified propylene polymer and about 55% to about75% of a solvent for a film forming resin material, wherein allpercentages are by weight based on the total weight of the powder, saidprocess comprising:a. dissolving a polar group-containing modifiedpropylene polymer at an elevated temperature in a solvent for the polargroup-modified propylene polymer, b. cooling the solution to precipitateparticles of the polar group-containing modified propylene polymer, c.replacing said solvent from said particles by contacting the particleswith a liquid which is capable of removing the solvent from theparticles, and d. collecting the particles.
 7. A process according toclaim 6 wherein the polar group-containing modified propylene polymer ismaleic anhydride modified polypropylene.
 8. A process according to claim6 wherein the solvent for the polar group-containing modified propylenepolymer is a mixture of isoparaffinic hydrocarbons.
 9. A processaccording to claim 6 wherein the liquid which is capable of removing thesolvent from the particles is methyl ethyl ketone.
 10. A processaccording to claim 6 wherein said replacement step (c.) results inparticles having less than about 5% by weight of said solvent for saidpolar group-containing modified propylene polymer relative to the weightof said modified propylene polymer.
 11. A process for preparing afree-flowing powder comprising about 25% to about 45% of particles of apolar group-containing modified propylene polymer and about 55% to about75% of a solvent for a film forming resin material, wherein allpercentages are by weight based on the total weight of the powder, saidprocess comprising:a. dissolving a polar group-containing modifiedpropylene polymer at an elevated temperature in a solvent for the polargroup-modified propylene polymer, b. cooling the solution to precipitateparticles of the polar group-containing modified propylene polymer, c.replacing said solvent from said particles by contacting the particleswith a liquid which is capable of removing the solvent therefrom, and d.collecting the particles, said step (a.) is being carried out at atemperature and concentration such that said precipitate particles havean average size of about 5 microns or less.
 12. A process according toclaim 11 wherein the polar group-containing modified propylene polymeris maleic anhydride modified polypropylene.
 13. A process according toclaim 11 wherein the solvent for the polar group-containing modifiedpropylene polymer is a mixture of isoparaffinic hydrocarbons.
 14. Aprocess according to claim 11 wherein the liquid which is capable ofremoving the solvent from the particles is methyl ethyl ketone.
 15. Aprocess according to claim 11 wherein said replacement step (c.) resultsin particles having less than about 5% by weight of said solvent forsaid polar group-containing modified propylene polymer relative to theweight of said modified propylene polymer.
 16. A process according toclaim 11 wherein the concentration in step (a.) is from about 1 to about15% by weight.
 17. A process according to claim 11 wherein theconcentration is step (a.) is from about 5 to about 10% by weight.
 18. Aprocess according to claim 6 wherein the powder produced and collectedin step (d.) has an average particle size of less than about 5 microns.